The problem we ran into
was that, in spite of the fact that we could lower the clock multiplier of our
CPUs from their default setting to all lower settings, we could not effectively
overclock the CPU by selecting a higher clock multiplier. Selecting a higher
clock multiplier would result in the system not even posting. We knew heat
was not an issue because running our 1GHz (10.0x) Thunderbird at 1050MHz (10.5x)
would not work while we could run the same CPU at the 105MHz FSB setting without
changing the clock multiplier (effectively 1050MHz) and it would work just fine.

Our home-made OVERRIDE pins on the FIC AZ-11

Because of this we concluded
that there was some other factor limiting us from increasing the clock multiplier,
most likely the CPU itself. Shortly after publishing the investigation we received
a few retail CPUs that we also tried in our
modified FIC AZ-11. The results were identical to the experience we had
with our “engineering samples” in that using the ‘FID’ jumpers we soldered onto
the AZ-11 would only allow us to underclock our CPUs but not increase their
clock multiplier above what they were shipped at. Increasing the clock multiplier
beyond their shipped state would result in the system not booting, which turned
out to be a hint as to exactly what was going on.